Only fill the water reservoir when you first use your Suvie. Fill up to the fill line indicated on the side of the reservoir (pictured above). Thereafter, only refill when you are prompted to. Only specific operations require water. While you will not need to refill from refrigeration frequently, you will periodically be prompted to due to evaporation additional internal water may be lost.
For the pans, you will need to fill them during Sous Vide and Egg modes. Fill so that the water envelops the vacuum-sealed bags (sous vide), or surrounds the egg pan without going over the top of them (egg mode).